This project will evaluate the feasibility of long-term fixation of prosthetic joint components by means of bone ingrowth into porous surfaces without the use of acrylic bone cement. Three porous metal systems will be evaluated; sintered cobalt chromium beads, sintered titanium 6-4 beads and sintered titanium 6-4 wire mesh. An established canine hip surface replacement model will be used. The canine model was developed during the first two years of an ongoing three-year project. Highly successful surgical procedures and histological techniques were developed and were used to evaluate numerous prosthetic fixation modes in 60 animals. With cemented prostheses cellular membranes invariably formed at the acrylic bone interface, a phenomenum associated with progressive loosening of components. In contrast, the porous systems showed good bone ingrowth with no membrane formation in up to 6 mos. follow-up. The problems that were encountered were primarily related to the overall design of the components. In the proposed project optimized design of both femoral and acetabular components with the three porous metal systems will be evaluated in the canine model with follow-up ranging from one month to two years. Analysis will include combined techniques of micro-radiography, fluorochrome labeling, electron and light microscopy and specially developed histological procedures. Loosening of cemented prosthetic joint components is currently the major cause of clinical failure. If the short-term promise shown by porous ingrowth fixation is fulfilled in the proposed long-term project, human application of these techniques would be justified to alleviate the rapidly growth number of clinical failures experienced with cemented joint replacements.